1. Field of the Invention
The present invention relates to a radio transmission system and method and, more particularly, to a radio transmission system and method configured to vary spreading factors for information symbol sequences according to cell environments or propagation environments, using the orthogonal frequency and code division multiplexing scheme.
The present invention also relates to transmitter apparatus used in such a radio transmission system.
The present invention further relates to receiver apparatus used in such a radio transmission system.
2. Related Background Art
The W (Wideband)-CDMA (Code Division Multiple Access) system was adopted as a radio access scheme in the third generation mobile telecommunication (IMT-2000: International Mobile Telecommunication 2000), and it was clarified by experiment that it was feasible to implement high-quality 2 Mbps transmission of less than average BER=10−6 in the 5 MHz band by means of this W-CDMA radio interface.
With recent progress in broadbandization of Internet services through wired networks, it is, however, considered that it is also necessary to realize high-speed mobile Internet access in cellular environments of mobile telecommunications. Since the data traffic is expected to increase because of downloading of images and large-volume files from Web sites and various databases, particularly, through downlinks by which data is transmitted from radio base stations and received at mobile stations, the essential is packet transmission suitable for up-down asymmetric communication and burst transmission.
Under such circumstances, proposals have been made on HDR (High Data Rate) specialized for data communication on the basis of the IS-95 radio interface and realizing high-speed packet transmission at the maximum information transmission rate of 2.4 Mbps in the 1.25 MHz band, and 3GPP (3rd Generation Partnership Project) also worked on the scheme of expanding the W-CDMA radio interface to realize high-speed packet transmission at the maximum information transmission rate of approximately 10 Mbps in the 5 MHz band (HSPDA: High Speed Down Link Packet Access). These schemes utilize the so-called adaptive modulation/demodulation technology of changing modulation/demodulation methods according to channel conditions, by which it becomes feasible to implement information transmission rates over 2 Mbps in good channel condition.